Method and apparatus for pressure expansion of tubing in coil assemblage

ABSTRACT

A tube pressure expansion device for expanding in unison tubes on a workpiece coil having plural fins. A coil holder holds the workpiece coil. A pressure expansion manifold has plural cavities each configured to receive a free end of a tube on the workpiece coil. An interior wall surface in each cavity has a tapered wall surface. A hollow tapered bullet is provided in each cavity and is configured for entering a tube opening at each free end for effecting an expansion of each free end to urge the material of each free end into a clamped and sealed relation with the interior wall surface in each cavity. A pressurized fluid is supplied to an interior of the hollow tapered bullet to effect a pressurization of the interior of the tubes to effect an expansion of the tubes into an interference fit with the fins on the workpiece coil.

FIELD OF THE INVENTION

This invention relates to a tube pressure expansion device and, more particularly, a device that is adapted to pressure-expand plural tubes embodied in a workpiece coil at the same time.

BACKGROUND OF THE INVENTION

It is known to expand the diameter of tubes by applying a pressurized fluid to the interior thereof so that the exterior surface thereof expands into contact with the fins of a heat exchanger coil for use in the heating, ventilating and air conditioning (HVAC) industry and U.S. Pat. No. 5,765,284 is a representative example. One of the problems faced by the manufacturers of the HVAC coils is to inexpensively pressure-expand a plurality of U-shaped tubes, known in the field as hairpin tubes, wherein the legs of the U-shaped tubes are each loosely laced through openings in the fins of the coil at the same time.

Accordingly, it is an object of this invention to facilitate the pressure-expansion of plural U-shaped tubes loosely laced through the fins of a HVAC coil so that the exterior surfaces of all of the U-shaped tubes are expanded into a tight fit with the internal diameter of the holes in the fins and all at the same time.

SUMMARY OF THE INVENTION

The objects and purposes of the invention are met by providing a tube pressure expansion device for expanding plural hollow tubes on a workpiece coil having plural fins. Each hollow tube has an open free end to an interior thereof. A pressure expansion manifold has plural cavities each configured to receive a free end of a respective tube on the workpiece coil. An interior wall surface in each cavity includes a tube seating wall surface. A hollow bullet is provided in each cavity and is configured for entering the tube opening at each free end for effecting an expansion of each free end to urge the material of each free end into a clamped and sealed relation with the tube seating wall surface in each said cavity. Plural passageways are provided in the pressure expansion manifold and each are configured to supply a pressurized fluid to an interior of each of the hollow bullets to effect a pressurization of the interior of each of the tubes to effect an expansion of the tubes into an interference fit with the fins on the workpiece coil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a tube pressure expansion device embodying the invention and illustrating an insertion of a workpiece coil into a coil holder;

FIG. 1A is an enlarged view of the encircled portion 1A illustrated in FIG. 1;

FIG. 2 is an isometric view of the tube pressure expansion device wherein the workpiece coil has been inserted into the coil holder;

FIG. 2A is an enlarged view of the encircled portion 2A illustrated in FIG. 2;

FIG. 3 is an isometric view of the tube pressure expansion device wherein the workpiece coil has been inserted into the coil holder and the access opening into the coil holder has been closed so that the workpiece coil is securely restrained within the coil holder;

FIG. 3A is an enlarged view of the encircled portion 3A illustrated in FIG. 3;

FIG. 4 is a front view of FIG. 3 and illustrating a start of a cycle of operation;

FIG. 4A1 is a partially sectioned enlargement of encircled part 4A1 in FIG. 4;

FIG. 4A2 is a further enlargement of a fragment of the encircled part 4A2 in FIG. 4;

FIG. 5 is a front view of the device wherein the pressure expansion manifold has been moved into a coupled relation with the tubes on the workpiece coil;

FIG. 5A1 is a partially sectioned enlargement of the encircled part 5A1 in FIG. 5 and illustrating a first phase of operation of the device;

FIG. 5A2 is a further enlargement of a fragment of the encircled part 5A2 in FIG. 5;

FIG. 5B1 is a partially sectioned enlargement of the encircled part 5B1 in FIG. 5 and illustrating a second phase of operation of the device wherein each of the free ends of the tubes has been cold worked into a clamped and sealed relation with the interior wall of the tube receiving cavity on the pressure expansion manifold;

FIG. 5B2 is a further enlargement of a fragment of the encircled part 5B2 in FIG. 5;

FIG. 5C1 is a partially sectioned enlargement of the encircled part 5C1 of FIG. 5 and illustrating a third phase of operation of the device;

FIG. 5C2 is a further enlargement of a fragment of the encircled part 5C2 in FIG. 5;

FIG. 6 is a front view of the device 3 wherein the pressure expansion manifold has been partially removed from the coupled relation with the tubes on the workpiece coil;

FIG. 6A1 is a partially sectioned enlargement of the encircled part 6A1 in FIG. 6;

FIG. 6A2 is a further enlargement of a fragment of the encircled part 6A2 in FIG. 6;

FIG. 7 is a front view of the device at the completion of a first cycle of operation depicted in the previous drawing figures;

FIG. 7A1 is a partially sectioned enlargement of the encircled part 7A1 in FIG. 7;

FIG. 7A2 is a further enlargement of a fragment of the encircled part 7A2 in FIG. 7;

FIG. 8 is a schematic representation of a conventional workpiece coil; and

FIG. 8A is a sectional view taken along the line 8A-8A in FIG. 8.

DETAILED DISCUSSION

Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “up”, “down”, “right” and “left” will designate directions in the drawings to which reference is made. The words “front”, “rear” will refer to the front and rear of a tube pressure expander device 10, the front thereof being the left side of FIG. 1. The words “in” and “out” will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Such terminology will include derivatives and words of similar import.

A typical workpiece coil WC (FIG. 8) consists of plurality of sheet metal fins F and a plurality of U-shaped tubes T as shown in FIG. 8A. The sheet metal fins F each have a plurality of holes H punched therethrough with upstanding collars C encircling each hole. The inner diameter of each hole H and surrounding collar C is larger than the diameter of the tubing forming the U-shaped tubes T. In this particular embodiment, the tubes T are oriented vertically and the fins F are loosely stacked thereon so that the next upper fin rests on the upper ends UE of the collars C as shown in FIGS. 8 and 8A. The U-shaped tubes T are, therefore, loosely laced into selected ones of the holes H to extend through the collars C to form the workpiece coil WC. The free ends of the legs L of the U-shaped tubes T are open to provide access to the interior of each of the U-shaped tubes T.

The tube pressure expansion device 10 is illustrated in FIGS. 1-7A2. Referring to FIG. 1, the tube pressure expansion device 10 includes a coil holder 11 composed of a bottom wall 12 having a plurality of sockets 13 for receiving therein the bight section BS of each of the U-shaped tubes T. The coil holder 11 additionally has an upstanding rear wall 14 formed by a pair, in this embodiment, of vertically spaced frame members 16 that are secured to a schematically illustrated support structure 15. Each of the frame members 16 have a pair of frontwardly extending supports 17A and 17B at each end of the frame members 16. A set of laterally spaced side guides 18A and 18B are mounted on the frontwardly facing side of the frame members 16 and inwardly from the respective supports 17A and 17B for the purpose of constraining the movement of the left and right edges 19A and 19B of the workpiece coil WC. Upstanding wall sections 21 in the form of doors are hingedly secured at one edge thereof as at 22 to each of the left frontwardly extending supports 17A so that the opposite edge of the doors will move toward and into engagement with the right frontwardly extending supports 17B and be releasably engage therewith by door locking devices not shown. It will be recognized that the doors 21 can be supported for movement by other configurations so as to allow access to the region of the coil holder 11 between the supports 17A and 17B.

A pair of elongate bars 20 extends coextensively along the front and back sides of the bottom wall 12 of the coil holder 11 and each is supported for movement by any conventional means, such as servos not illustrated, toward and into engagement with the front and back walls of the bottom wall 12 as well as away therefrom. Each bar 20 has a plurality of pin-like extensions 25 thereon that have a half cylindrical downwardly facing surface 25A (see also FIG. 8) that are each configured to enter the sockets 13 and become positioned above the respective bight sections BS to lock the bight sections to the bottom wall in response to the bars 20 being moved into engagement with the front and back walls of the bottom wall 12 as shown in FIG. 3A.

The tube pressure expansion device 10 includes a pressure expansion manifold 23 supported for movement toward and away from the coil holder 11 and relative to the support structure 15. Referring to FIG. 5A, the manifold 23 includes a plurality of chambers 24, cavities 26 and elongate bores 27 each interconnecting a respective pair of chambers 24 and cavities 26. In this particular embodiment, the respective pairs of chambers 24 and cavities 26 are vertically spaced from one another so that all of the elongate bores 27 extend in parallel relation between the respective pairs of chambers 24 and cavities 26.

Each cavity 26 includes a hollow sleeve insert 28 wherein the interior thereof has a cylindrical upper interior surface segment 29, a tapered mid-interior surface segment 31 and a cylindrical lower surface segment 32. The cylindrical lower interior surface segment 32 is of a sufficient interior diameter selected to receive therein with minimal clearance the exposed end, here a cylindrical end CE (FIG. 8), of each tube T on the workpiece coil WC. The tapered mid-interior surface segment 31 is smooth and inclined to a longitudinal axis of each cavity 26 and extends from a small diameter dimension at an upper terminal end of the cylindrical lower interior surface segment 32 to a larger diameter dimension terminating at a lower terminal end of the cylindrical upper interior surface segment 29. In this particular embodiment, the interior diameters of the bores 27 and the cylindrical upper interior surface segment 29 are the same.

Reciprocal rams 33 are received in each of the serially linked chambers 24, elongate bores 27 and cavities 26. Each ram 33 includes a piston 36 which is reciprocally received in each of the chambers 24, an elongate hollow piston rod 37 which is connected to each piston 36 and extends to a distal end 38 located in each cavity 26 and whereat there is connected a hollow a tapered bullet 39. The hollow interior 41 of the piston rod 37 and the hollow interior 42 of the tapered bullet 39 are interconnected. Further, the hollow interior 41 of the piston rod 37 includes a crosswise extending passageway 40 opening outwardly of the piston rod at a location about midway between the chambers 24 and the cavities 26. Each exterior surface 43 of each tapered bullet 39 is smooth and tapered and is inclined to the longitudinal axis of the respective cavity 26 in the same direction as is the tapered mid-interior surface segment 31. The exterior surface diametrical dimension along an axial length of each exterior surface 43 is less than the corresponding interior surface diametrical dimension of the tapered mid-interior surface segment 31 by a dimension that is just slightly less than the thickness of the material of the exposed cylindrical end CE of each of the tubes T on the workpiece coil WC. The purpose of this dimension difference will become apparent in the following description.

Each chamber 24 has an access opening 34 thereto in the manifold 23 to facilitate assembly. The openings 34 are each closed by a plug 35.

A first passageway 46 extends through the manifold 23 and opens into each chamber 24 at a location oriented on an upper side of each piston 36. A second passage way 47 extends through the manifold 23 and opens also into each chamber 24 at a location oriented on an opposite side of each piston 36. A third passageway 48 extends through the manifold 23 and opens into each bore 27 just below the location whereat the crosswise extending passageway 40 opens into the bores 27. The passageways 46, 47 and 48 are only schematically illustrated in FIGS. 4A, 5A-5C, 6A and 7A.

A control device 50 is provided to control the sequence of operation of the tube pressure expansion device 10, including the servos that move the bars 20 toward and away from the bottom wall 12. A first valve 51 is a solenoid operated valve wherein the solenoid 52 thereof is connected to the control device 50. In this particular embodiment, the solenoid 52 is an electric solenoid and it is electrically connected to the control device 50 by an electrical line 53. The valve 51 illustrated in the drawings is representative of a three position hydraulic valve. The three positions of the valve 51 will be explained in more detail below.

A second valve 56 is also a solenoid operated valve wherein the solenoid 57 thereof is connected to the control device 50. In the particular embodiment, the solenoid 57 is an electric solenoid and it is electrically connected to the control device 50 by an electrical line 58. The valve 56 illustrated in the drawings is a representative of a two position hydraulic or pneumatic valve. The two positions of the valve 56 will be explained in more detail below.

A source S1 of pressurized hydraulic fluid is connected to the valve 51 through a conduit 54. A return line to tank is provided through the conduit 55. A source S2 of pressurized air, oil, nitrogen, water, argon or the like is connected to the valve 56 through a conduit 59. If a gas is used as the pressurized fluid from the source S2, there need be no return line to a tank from which the gas emanates and such is illustrated in FIGS. 5A-5C. On the other hand, and if desired, it will be understood that the valve 56 could be, instead, a three position valve (not shown) directing the exhaust gas to exit through the valve to a sound muffling device (also not shown) to facilitate a minimizing of the noise of escaping gas.

A hydraulic cylinder 61 (FIG. 1) is supported on the support structure 15 of the tube pressure expansion device 10 and includes a reciprocal piston rod 62 connected to the manifold 23 to move the manifold toward and away from the coil holder 11 as will be explained in more detail below. A third valve 63 is provided and is a solenoid operated valve wherein the solenoid 64 thereof is connected to the control device 50. In this particular embodiment, the solenoid 64 is an electric solenoid and it is electrically connected to the control device 50 by an electrical line 66. The valve 63 is a three position hydraulic valve like the valve 51.

A source S3 of pressurized hydraulic fluid is connected to the valve 63 through a conduit 67. A return line to tank is provided through the conduit 68. A conduit 71 extends from the valve 63 to the upper end of the hydraulic cylinder and a further conduit 72 extends from the valve 63 to the lower end of the hydraulic cylinder. Pressurized hydraulic fluid supplied to the conduit 71 and to the upper end of the cylinder 61 will cause the piston rod 62 to drive the manifold 23 toward the coil holder 11.

Operation

While persons skilled in the art will understand the operation of the tube pressure expansion device based on the above description, a brief summary of the operation is being provided for convenience.

As is illustrated in FIGS. 1-3, a workpiece coil is inserted into the coil holder between the supports 18A and 18B through the opened doors 21 and so that the bight sections BS enter the sockets 13 provided therefor in the bottom wall 12. Thereafter, the doors 21 are closed as depicted in FIG. 3 and latched by conventional door locking devices not shown. Next, the control device 50 is activated to cause the pressure expansion manifold 23 to be lowered from the FIGS. 4, 4A1 and 4A2 position to the FIG. 5, 5A1 and 5A2 position wherein each of the upstanding tubes T enter a respective cavity 26 and each of the tapered bullets 39 in each of the cavities enter a respective open end of a tube T to thereby cause the exterior surfaces 43 on each bullet 39 to effect an initial cold working movement of the tube material on an axial section adjacent each the free ends radially outwardly so that the outer surfaces of each axial section engages the tapered mid-section of the sleeve insert 28. Next, the control device 50 activates the valve 51 to shift it from a neutral central position to a first operative position depicted in FIGS. 5B1 and 5B2 to direct pressurized fluid from the source S1 to the upper region of the chambers 24 and on one side of the pistons 36 to drive the pistons toward the workpiece coil WC. This movement of the pistons 36 simultaneously causes the tapered bullets 39 to enter further into the open free ends of the tubes T to compress the material of the aforesaid axial sections of the free end between the tapered exterior surfaces 43 on each of the tapered bullets 39 and the tapered mid-surfaces 31 on each of the sleeve inserts 28 and form a seal thereat. The control device 50 also activates the valve 56 to shift it from the neutral position to the operative position thereof to direct pressurized fluid from the source S2 to each of the crosswise extending passageways 40, the hollow interior 37 of the piston rod 37 and thence to the hollow interior 42 of the tapered bullets 39 and the interior of each of the tubes T. The pressure of the pressurized fluid from the source S2 is sufficient to expand the diameter of all of the tubes at the same time causing the exterior surfaces thereof to form an interference fit with the inner surfaces of the holes H and the collars C in each of the fins F as shown by the broken lines at T′ in FIG. 8A representing an expanded tube. Next, the control device 50 deactivates the valve 56 shutting off the supply of pressurized fluid from the source S2 while simultaneously causing a discharging of some or all of the pressurized gas to atmosphere. The valve 51 will then be activated to reverse the supply of pressurized fluid from the source S1 to a region of the chambers 24 at an opposite side of the pistons 36 to return the pistons to the position depicted in FIGS. 5C1 and 5C2 corresponding to the original starting position depicted in FIGS. 5A1 and 5A2 to retract the tapered bullets 39 a small distance but remain inside the free ends of each of the tubes T so as to relieve the mechanical locking or clamping pressure inside the tubes T. Thereafter, the control device 50 effects a movement of the pressure expansion manifold away from the workpiece coil WC to the FIGS. 6, 6A1 and 6A2 position wherein the tapered bullets 39 are each withdrawn from the free ends of the tubes T and simultaneously cold work the axial section at the free ends CE of each of the tubes T back to their original cylindrical shape. Thereafter, the control device 50 effects a movement of the pressure expansion manifold to the starting position depicted in FIGS. 7, 7A1 and 7A2 and FIGS. 4, 4A1 and 4A2. Movement of the workpiece coil WC and particularly the U-shaped tubes T during a withdrawal of the tapered sleeve inserts 28 from the free ends of the tubes T while the free ends are being cold worked to a cylindrical shape will be prevented by the retention of the workpiece coil WC in the coil holder 11 by engagement of the respective surfaces 25A on each of the pins 25 on the bars 20 with the bight sections BS on each tube as shown in FIG. 8. Thereafter, the control device 50 will initiate a sequenced movement of the bars 20 away from the bottom wall 12 to pull the pins 25 away from the bight sections BS. An operator (or robot) may now open the doors 21 and remove the finished workpiece coil WC from the coil holder 11.

The tube expansion process described above causes a radial outward expansion of the tube material. Since the bight sections BS of each tube is retained in place by the cooperative relationship between the pins 25A (FIG. 8) and the sockets 13 in the bottom wall 11, the tubes will want to shrink in length but such shrinkage will be prevented or reduced by the aforesaid structure. This has the advantage that only the wall thickness of the tubes will shrink and the tube expansion process occurs while the tubes are held by the clamping of the material at the free ends between the tapered surfaces 31 and 43 at one end of the U-shaped tubes and by the sockets 13 and cooperating pins 25A at the bottom wall 12 on the bight sections BS. If desired, the tension forces on the tubing during the expansion process can be lessened by the manifold being controlled by the control device 50 to urge the manifold further toward the workpiece coil as the tube expansion process is being performed.

Although particular preferred embodiments of the invention have been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention. 

What is claimed is:
 1. A tube pressure expansion device for expanding plural hollow tubes on a workpiece coil having plural fins, each hollow tube having an open free end to an interior thereof, comprising: a pressure expansion manifold having plural cavities each configured to receive a free end of a respective tube on the workpiece coil, an interior wall surface in each cavity including a tube seating wall surface; a hollow bullet provided in each said cavity and being configured for entering the tube opening at each free end for effecting an expansion of each free end to urge the material of each free end into a clamped and sealed relation with said tube seating wall surface in each said cavity; plural passageways in said pressure expansion manifold each configured to supply a pressurized fluid to an interior of each said hollow bullet to effect a pressurization of the interior of each of the tubes to effect an expansion of the tubes into an interference fit with the fins on the workpiece coil.
 2. The tube pressure expansion device according to claim 1, wherein said plural passageways are configured to supply the pressurized fluid in unison to said interior of said hollow bullet.
 3. The tube pressure expansion device according to claim 1, wherein each said tube seating wall surface in each said cavity is tapered and each hollow bullet has a tapered outer surface.
 4. The tube pressure expansion device according to claim 1, wherein each said hollow bullet includes a piston and a hollow piston rod interconnecting said hollow bullet to said piston, and each said cavity includes a chamber and an elongate bore interconnecting said chamber to said tube seating wall surface region in said cavity, said piston being reciprocally supported in said chamber, said piston rod being reciprocally supported in said bore and said hollow bullet being reciprocally supported in said tube seating wall surface region of said cavity.
 5. The tube pressure expansion device according to claim 4, wherein said plural passageways in said pressure expansion manifold each configured to supply a pressurized fluid to each said hollow piston rod and thence to said interior of each said hollow bullet to effect a pressurization of the interior of each of the tubes to effect an expansion of the tubes into an interference fit with the fins on the workpiece coil.
 6. The tube pressure expansion device according to claim 5, wherein a plurality of further passageways are provided in said pressure expanding manifold configured to supply a further pressurized fluid to said chamber selectively drive said plural interconnected pistons, said hollow piston rods and said hollow bullets toward and away from said free ends.
 7. The tube pressure expansion device according to claim 6, wherein said further passageways includes a valve and a control means for controlling said valve to effect a supply of said further pressurized fluid to each of said chambers and a first side of each of said pistons to drive each of said pistons toward said workpiece coil to thereby cause said hollow bullet to be driven into the open free ends of each of the tubes to expand the material of each free end into a clamped and sealed relation with said tube seating wall surface in each said cavity.
 8. A tube pressure expansion device for expanding in unison a first outer diameter of each of a plurality of separate U-shaped tubes on a workpiece coil consisting of a plurality of stamped fins having a plurality of spaced apart holes therethrough, each hole being of a second inner diameter greater than the first diameter surrounded by an upstanding collar, said stamped fins being stacked on top of one another and separated from one another, legs of the U-shaped tubes being loosely laced through selected ones of the holes and collars so that free ends of the tube legs extend outwardly from one side of the coil and bight sections between respective pairs of the tube legs extend outwardly from a side of the coil remote from the aforesaid one side, comprising: a coil holder configured to hold the workpiece coil in a stationary position, said coil holder having a bottom wall configured to physically restrain all of the bight sections and plural wall sections configured to physically restrain the workpiece coil, support means for supporting one of said plural wall sections for movement between opened and closed positions to facilitate an insertion and removal of said workpiece coil into and from said coil holder; a pressure expansion manifold supported for movement between first and second positions in response to said one of said plural wall sections being in said closed position so that said workpiece coil and said bight sections are physically restrained in said coil holder, said pressure expansion manifold having plural cavities therein each configured to receive therein a respective free end of a tube leg, an interior wall surface in each said cavity having a tapered wall surface, said first position of said pressure expansion manifold being spaced from said free ends, said second position corresponding with said free ends being received in said cavities; plural hollow reciprocating rams on said pressure expansion manifold each having thereon a hollow tapered bullet located in each said cavity, each said tapered bullet being configured for entering a tube opening at each free end for effecting an expansion of the first outer diameter at each said free end to urge the material of each free end into a clamped and sealed relation with said interior wall surface in each said cavity; a first supply of a first pressurized fluid; a plurality of first passageways in said pressure expanding manifold configured to supply said first pressurized fluid to each said cavity to selectively drive said plural hollow reciprocating rams and said hollow tapered bullets therewith toward and away from said free ends; a second supply of a second pressurized fluid; and a plurality of second passageways configured to selectively supply the second pressurized fluid to an interior of each said hollow reciprocating rams and thence to an interior of said hollow tapered bullets in response to said pressure expansion manifold being located in said second position and each free end is in a clamped and sealed relation with said interior wall surface in each said cavity to thereby effect a pressurization of the interior of each of the U-shaped tubes and an expansion of the first outer diameter of the tubes into an interference fit with each hole and collar on said stamped fins on said workpiece coil.
 9. The tube pressure expansion device according to claim 8, wherein each hollow reciprocating ram includes a piston and a piston rod having a hollow tapered bullet oriented at a distil end of said piston rod remote from said piston, said pressure expansion manifold including plural chambers each having an elongate bore opening into said chamber at one end and said cavity at an opposite end, said piston being reciprocally supported in said chamber, said piston rod being reciprocally supported in said bore and said tapered bullet being reciprocally supported in said cavity.
 10. The tube pressure expansion device according to claim 9, wherein said plural first passageways connect said first supply to said chamber on opposite sides of said pistons in each of said chambers.
 11. The tube pressure expansion device according to claim 10, wherein said first supply includes a first valve and control means for controlling said first valve to effect a supply of said first pressurized fluid to each of said chambers and a first side of each of said pistons to drive each of said pistons toward said workpiece coil to thereby cause each said tapered bullet to be driven into the open free ends of each of the tubes to expand the first outer diameter at each free end to urge the material of each free end into a clamped and sealed relation with said interior wall surface in each said cavity.
 12. The tube pressure expansion device according to claim 11, wherein said second supply includes a second valve controlled by said control means to effect a supply of said second pressurized fluid to said an interior of each of said hollow piston rods and thence to an interior of each of said tapered bullets and an interior of each of the U-shaped tubes to thereby effect a pressurization of the interior of each of the U-shaped tubes for a finite period of time to cause an expansion of the first outer diameter of the tubes into an interference fit with each hole and collar on said stamped fins on said workpiece coil.
 13. The tube pressure expansion device according to claim 12, wherein said control means is configured to control at a conclusion of said finite period of time said second valve discharge of some or all of the supply of said second pressurized fluid followed by said first valve switching to direct said first pressurized fluid to said second side of each of said pistons to drive each of said pistons away from said workpiece coil to thereby cause said tapered bullet to be partially withdrawn from the open free ends of each of said tubes to at least partially relieve the internal mechanical clamping pressure inside said U-shaped tubes.
 14. The tube pressure expansion device according to claim 1, wherein each said tube seating wall surface in each said cavity is tapered and each hollow bullet has a tapered outer surface, an end of said taper remote from said chamber 24 terminating in a cylindrical shaped opening sized to cold work the material of the free ends of the tubes as said manifold is removed from engagement with the workpiece coil.
 15. A method for tube pressure expansion of plural hollow tubes on a workpiece coil having plural fins, each hollow tube having an open free end to an interior thereof, comprising: moving a pressure expansion manifold having plural cavities each configured to receive a free end of a respective tube on the workpiece coil toward a workpiece coil so that the free end of each tube is received in a respective cavity in the manifold, an interior wall surface in each cavity including a tube seating wall surface; moving a hollow bullet provided in each said cavity relative to said manifold into each tube opening at each free end for effecting an cold working expansion of each free end to urge the material of each free end into a clamped and sealed relation with said tube seating wall surface in each said cavity; supplying plural passageways in said pressure expansion manifold with a pressurized fluid and to an interior of each said hollow bullet to effect a pressurization of the interior of each of the tubes to effect an expansion of the tubes into an interference fit with the fins on the workpiece coil.
 16. The method according to claim 15, wherein said moving said pressure expansion manifold includes a movement of said manifold away from the workpiece coil after a completion of a tube expansion to draw the free ends of the tubes through a cylindrical opening into each cavity to return the free ends to a cylindrical shape. 